What happens after CVS is done?
You are advised to rest at home for the remainder of
the day following the CVS. If you have a Rh negative
blood group you will receive an injection of Anti D at
the end of the procedure. Your doctor will explain
why this is necessary.
You will be contacted with the results from your test.
Ongoing care will be arranged either at the WCHN or
with your referring team.
The Results from your CVS
The most common test done on a CVS sample is a
chromosome test. There are several methods that
can check for abnormalities of the chromosomes.
• A FISH test screens for some common major
chromosome abnormalities by providing a
rapid count of certain chromosomes
(13,18,21,X and Y) Results are usually
available in 1-2 days.
• A Karyotype tests for large extra or missing
pieces of chromosome material using a
microscope.
• A Microarray tests for both large and very
small extra or missing pieces of
chromosome material using a DNA based
test.
In some cases, tests for specific genetic conditions
may also be done on the CVS sample.
Your doctor will discuss the different options with you
before a decision is made which method will be used
to test your CVS sample. Final results will usually be
available after 7-10 days.
The CVS will identify the sex of the baby. Parents
may choose whether or not they wish to be told.
In a small number of cases, a chromosome test may
need to be done on a blood sample on you and your
partner to help interpret the CVS result.
Occasionally further tests may also be needed on the
baby. In about 2 in 100 tests (2%) the results may
be difficult to fully interpret and an amniocentesis
may be needed to clarify the results. (See brochure
on amniocentesis).
Are There Other Tests that can tell whether
my baby has a chromosome problem?
Amniocentesis is another test that allows a baby’s
chromosomes to be tested accurately. This test can
be done after 15 weeks of pregnancy. Please read
the brochure on amniocentesis for further information
about the differences between these tests. It is usual
to choose either a CVS or an Amniocentesis, not
both.
Does a normal CVS result mean that my
baby will be born healthy?
CVS is an accurate way of testing for most
chromosome abnormalities. However, mosaicism
and very small chromosome abnormalities cannot be
excluded. (see introductory brochure on ‘testing for
birth defects in pregnancy’)
A CVS cannot detect all problems with a baby. A
normal CVS result does not exclude all birth defects
or genetic conditions, as most are caused by changes
in specific genetic instructions which require more
specialised tests to detect.
What if the test shows that my baby has a
problem?
If the test shows that your baby has a problem, a
medical specialist will talk to you about what this is
likely to mean for the baby and what treatments or
options are available to you.
For more information
Maternal Fetal Medicine
Monday – Friday 8.30am – 4.30pm
(08) 8161 9263
Fax: (08) 8161 9264
72 King William Road
North Adelaide
South Australia 5006
Phone (08) 8161 7000
Web: http://www.wch.sa.gov.au
(Revised) June 2021
Chorionic
Villus
Sampling
(CVS)
Women’s & Children’s
Hospital
CHORIONIC VILLUS SAMPLING (CVS)
This brochure explains a procedure called
Chorionic Villus Sampling (CVS) that is available
in pregnancy. It is one of a number of ways that
chromosome abnormalities and genetic
conditions can be detected in pregnancy.
What is CVS
CVS is a procedure that collects a small sample of the
developing placenta (‘after-birth’). Cells from the
placenta usually have the same genetic make-up as
those from the baby. The placental tissue collected is
called chorionic villus. Different types of genetic tests
can be done on the CVS sample, depending on why the
test is being done.
The most common test done on a CVS sample is a
chromosome test. Chromosomes are tiny structures in
the cells of the body that contain the genetic
instructions for growth and development. CVS can be
used to check for abnormalities of the chromosomes,
such as a whole extra or missing chromosome, or extra
or missing pieces of the chromosomes, which can cause
physical and learning disabilities.
In some cases, tests for specific genetic conditions may
also be done on the CVS sample.
Why should I consider CVS in my Pregnancy?
CVS may be offered when there is an increased chance
that the baby may have a genetic condition. Some of
the most common reasons include:
• If an increased chance of a chromosome abnormality
is identified on a screening test, such as nuchal
translucency screening, first trimester screening or
non invasive prenatal testing.
• If an ultrasound detects a physical abnormality in the
baby.
• If the parents have had a previous baby with a
chromosome abnormality, or a parent has a variation
of the chromosomes that increases the chance of the
baby having a chromosome abnormality.
• If there is an increased chance that the baby may
have a particular genetic disorder, for which testing
is available
It is up to you and your partner whether you choose to
have a CVS. You can discuss this with your doctor or
midwife.
When is CVS done?
CVS is usually done between 11 to 14 weeks of
pregnancy.
How is CVS done?
CVS is an outpatient procedure performed by a specially
trained doctor. If you decide to have a CVS, an
ultrasound scan will be arranged before the test to
confirm the due date of your pregnancy. Your blood
group will also be checked by a blood test.
It is useful to have a full bladder for the CVS, as this can
help position the uterus (womb) to allow easier access
to the placenta. Starting an hour before the scan you
will need to drink 300 -500ml of clear fluid (not milky or
fizzy), finishing half an hour before the scan. The CVS
procedure takes about 30 minutes. Most of the time
involves having an ultrasound scan and preparing
equipment. The collection of the sample usually takes
about a minute.
Your partner or support person is encouraged to attend.
It is best that children do not attend. Creche facilities
are available free of charge at the hospital, ring 8161
6394 to book.
The Procedure
Ultrasound is used to see where the placenta is
located. Your abdomen (tummy) will be cleaned with
antiseptic, and a local anaesthetic used to numb your
skin. A needle is then inserted through your
abdomen and into the placenta. An ultrasound is
used at all times to watch the needle path. A syringe
is then attached to the end of the needle and the
sample obtained. The placental sample is sent to the
laboratory for testing.
Sometimes due to the position of the placenta, it
may not be possible to collect a sample. If this
happens, you may be asked to return in one or two
weeks. If a CVS is not possible at that time, then a
different test called amniocentesis may be needed.
(See brochure on Amniocentesis)
Most women say that the procedure is no more
painful than other types of injections. Some women
feel cramping when the needle enters the uterus or
pressure as the sample is being collected.
What are the risks of having a CVS
for the woman and baby?
Some women experience abdominal cramping on the
day of the test. This usually settles within 24 hours
and should be relieved with simple pain relief like
Panadol. If the pain is increasing or if you have any
bleeding or fluid loss from the vagina you should
contact your doctor, or call Women’s Assessment
Service on 8161 7530.
There is a small risk of miscarriage following CVS.
Current literature suggests that less than 1 woman
in every 300 will miscarry as a result of having a
CVS. In other words less than 0.5% of all women
who have this test will miscarry
